Lubricating oil supplying system for internal combustion engine

ABSTRACT

A lubricating oil supplying system for an internal combustion engine includes a lubricating oil storage section for storing lubricating oil. A driven pump is driven by the internal combustion engine to suck the lubricating oil from the lubricating oil storage section and discharge the lubricating oil to a discharge passage. An electric pump is provided for sucking the lubricating oil discharged from the driven pump to the discharge passage and discharge the lubricating oil to a lubricating oil requiring section in the internal combustion engine. A controlling mechanism is provided for drivingly controlling the electric pump in accordance with a control signal. A bypass passage is provided for bypassing the driven pump. A check valve is disposed in the bypass passage to allow the lubricating oil in the lubricating oil storage section to flow only through a path bypassing said driven pump and toward side of the discharge passage.

BACKGROUND OF THE INVENTION

This invention relates to improvements in a lubricating oil supplyingsystem for an internal combustion engine, arranged to supply lubricatingoil to various sliding sections, a variable valve actuation mechanism orthe like in the internal combustion engine under the action of an oilpump driven by the internal combustion engine and an electric pumpdriven by an electric motor.

Hitherto, various types of the lubricating oil supplying systems areproposed and put into practical use. One of such lubricating oilsupplying apparatuses is disclosed in a Japanese Patent ProvisionalPublication No. 2003-148120. Briefly, this lubricating oil supplyingsystem includes a variable valve actuation mechanism serving as adriving device, disposed to a main body of an internal combustionengine. A variable valve actuation mechanism and various slidingsections are supplied with lubricating oil stored in a lubricating oiltank. The lubricating oil stored within the above lubricating oil tankis sucked and supplied to the above main body of the internal combustionengine or the like, under the action of a driven pump driven by theinternal combustion engine.

The lubricating oil supplying system further includes a heataccumulative container which is in communication with the discharge sideof the above driven pump and stores therein the lubricating oildischarged from the above driven pump, warming the lubricating oil. Thelubricating oil within the above heat accumulative container is suckedand supplied to the above variable valve actuation mechanism and thelike under the action of an electric pump disposed separate from theabove driven pump. Consequently, the above electric pump and variousopening-closing valves are driven through a control means in accordancewith a prediction result of a starting prediction means for the internalcombustion engine, thereby supplying the lubricating oil, which has beenpreviously heated before the starting of the internal combustion engine,to the variable valve actuation mechanism so as to improve a drivingresponse of the engine.

SUMMARY OF THE INVENTION

In the above conventional lubricating oil supplying system, the aboveelectric pump is disposed at the downstream side of the driven pump andlocated in series with the driven pump through the above heataccumulative container, so that the lubricating oil sucked in anddischarged from the driven pump is directly sent to the electric pump.Consequently, it is not required that each pump separately suckslubricating oil from the lubricating oil tank. As a result, there is amerit of simplifying a hydraulic circuit. However, if the amount of thelubricating oil discharged from the driven pump exceeds that from theelectric pump, a negative pressure is developed between these pumps. Inview of this, a check valve is provided to the above heat accumulativecontainer to introduce a low pressure therein, so that the abovenegative pressure can be prevented from being developed.

However, during opening of the above check valve, the lubricating oil issupplied into the above heat accumulative container through a hydraulicpassage formed separate from the above configuration in order to fillthe above heat accumulative container with the lubricating oil. Thishydraulic passage must be formed relatively long, so that the structureof oil pressure passages is complicated. As a result, manufacturing orproduction operation for the lubricating oil supplying system becomestroublesome so that a production cost unavoidably rises.

It is an object of the present invention is to provide an improvedlubricating oil supplying system for an internal combustion engine whichcan effectively overcome drawbacks encountered in conventionallubricating oil supplying systems for the internal combustion engine.

Another object of the present invention is to provide an improvedlubricating oil supplying system for the internal combustion engine, inwhich a negative pressure can be prevented from being developed betweena driven pump and an electric pump for lubricating oil supply, whileavoiding complication of a passage structure for the lubricating oilthereby suppressing a rise in production cost.

An aspect of the present invention resides in a lubricating oilsupplying system for an internal combustion engine, which includes alubricating oil storage section for storing lubricating oil. A drivenpump is driven by the internal combustion engine to suck the lubricatingoil from the lubricating oil storage section and discharge thelubricating oil to a discharge passage. An electric pump is provided forsucking the lubricating oil discharged from the driven pump to thedischarge passage and discharge the lubricating oil to a lubricating oilrequiring section in the internal combustion engine. A controllingmechanism is provided for drivingly controlling the electric pump inaccordance with a control signal. A bypass passage is provided forbypassing the driven pump. A check valve is disposed in the bypasspassage to allow the lubricating oil in the lubricating oil storagesection to flow only through a path bypassing said driven pump andtoward side of the discharge passage.

With the above arrangement, when an amount of the lubricating oildischarged from the driven pump exceeds that from the electric pump, thelubricating oil within the lubricating oil storage section is flowedfrom the inlet of the bypass passage through the check valve into theside of the above discharge passage. Then, the lubricating oil is suckedin and discharged from the electric pump so as to be supplied to thelubricating oil requiring section. By this, a negative pressure can beprevented from being developed between the both pumps, while avoidingcomplication of a passage structure for the lubricating oil therebysuppressing a cost rise, because only the short bypass passage formerely bypassing driven pump is provided.

Another aspect of the present invention resides in a fluid pump, whichincludes a pump mechanism for sucking fluid from a storage section anddischarging the fluid to a discharge section. A plunger valve body has apressure receiving section which is formed at one end side of theplunger valve body and opens to the discharge section. The plunger valvebody is movable to release a part of fluid discharged from the pumpmechanism to the discharge section to a low pressure section. A sectiondefining a low pressure chamber is formed at the other end side of theplunger valve body and in communication with the low pressure section. Abiasing member is disposed in the low pressure chamber to bias theplunger valve body in one direction. A check valve is disposed in thepressure receiving section of the plunger valve body to allow thelubricating oil to flow through a path from the lower pressure chamberto the discharge section.

A further aspect of the present invention resides in a lubricating oilsupplying system for an internal combustion engine, which includes alubricating oil storage section for storing lubricating oil. A firstpump is provided for sucking the lubricating oil from the lubricatingoil storage section and discharging the lubricating oil to a dischargepassage. A second pump is provided for sucking the lubricating oildischarged from the first pump to the discharge passage and dischargingthe lubricating oil to a lubricating oil requiring section in theinternal combustion engine. A bypass passage is provided for bypassingthe first pump. An opening and closing mechanism is disposed in thebypass passage to open the bypass passage when an amount of thelubricating oil discharged from the first pump exceeds that from thesecond pump, and to cutoff the bypass passage when the amount of thelubricating oil discharged from the first pump is similar to that fromthe second pump or when the amount of the lubricating oil dischargedfrom the second pump is lower than that from the first pump.

The other objects and features of this invention will become understoodfrom the following description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference numerals designate like parts andelements throughout all figures in which:

FIG. 1 is a diagrammatic illustration of an oil pressure circuit of anembodiment of a lubricating oil supplying system according to thepresent invention;

FIG. 2 is a perspective view of a variable valve actuation mechanismused in the system of FIG. 1;

FIG. 3 is a front view of an oil pump used in the system of FIG. 1;

FIG. 4 is a vertical cross-sectional view of an assembly arrangementincluding a relief valve and a check valve in another embodiment of thelubricating oil supplying system according to the present invention; and

FIG. 5 is a plan view of a plunger valve body used in the relief valveof FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 to 5, an embodiment of a lubricating oilsupplying system for internal combustion engine, according to thepresent invention is illustrated. Firstly, the internal combustionengine is a multi-cylinder V-type engine, in which two intake valves 1,1 are provided for each (engine) cylinder so as to be slidably supportedby a cylinder head (not shown). The valve lift of each intake valves 1,1 is variably controlled in accordance with an engine operatingcondition under the action of a variable valve lift mechanism 2 as shownin FIG. 2.

This variable valve lift mechanism 2 is the same as that disclosed inJapanese Patent Provisional Publication No. 2001-214765 whose assigneeis the same as that in the present application, so that explanationthereof will be briefly made. Japanese Patent Provisional PublicationNo. 2001-214765 is incorporated herein by reference. In the variablevalve lift mechanism 2, driving shaft 3 whose inside is hollow isarranged at the side of each bank side of the engine to extend in thefore-and-aft direction of the engine. Cam shaft 4 is provided for eachcylinder in such a manner as to be movably supported around the outerperipheral surface of above driving shaft 3 and coaxial with drivingshaft 3. Driving cam 5 is fixedly disposed at a certain position ofabove driving shaft 3 and provided for each cylinder. A pair ofswingable cams 7, 7 are fixed to above cam shaft 4 at opposite endsections and slidably contacted with valve lifters 6, 6 which arerespectively disposed at upper end sections of intake valves 1, 1, so asto make opening action of intake valves 1, 1. Locker arm 8 links drivingcam 5 to swingable cam 7 and serves as a transmission means fortransmitting torque of driving cam 5 as swingable force (or valveopening force) to swingable cams 7, 7. Link arm 9 mechanically links oneend of locker arm 8 to the above driving cam 5. Link rod 10 mechanicallylinks the other end of locker arm 8 to the above swingable cam 7. Acontrol means is provided to control an operational position of thetransmission means.

The above control means includes control shaft 11 which is movablysupported above driving shaft 3. Control cam 12 is fixed, as a singlemember, on control shaft 11 at outer peripheral surface so as to serveas a swingable supporting section of above locker arm 8. Above controlshaft 11 is rotatably controlled by hydraulic actuator 13 within acertain rotational angle range.

Above hydraulic actuator 13 includes hydraulic cylinder 14 installed toan end wall of the cylinder head (not shown) through a bracket (notshown). Piston 15 is slidably disposed in hydraulic cylinder 14 todivide an interior of hydraulic cylinder 14 into two hydraulic chambers16 a, 16 b. Piston rod 17 has its one end section fixed with piston 15,and the other end section linked with above control shaft 11 throughlinking arm 18. Oil pressure is supplied to or released from the abovelubricating oil supplying system selectively into above hydraulicchambers 16 a, 16 b.

As shown in FIG. 1, the above lubricating oil supplying system includesoil pan 20 (or a low pressure section) as a lubricating oil storagesection at a low pressure side, installed at a lower end section of acylinder block (not shown) of the internal combustion engine in order tostore lubricating oil (or hydraulic fluid). One-way oil pump 22 as adriven pump is rotationally driven by a crankshaft (not shown), andsucks the lubricating oil from above oil pan 20 through strainer 21 andsuction passage 23. One-way electric pump 25 is connected in series withoil pump 22, and sucks the lubricating oil discharged through oil pump22 to discharge passage 24 (or a discharge section) directly via secondsuction passage 26 and discharges the lubricating oil to seconddischarge passage 27. The lubricating oil discharged from electric pump25 through second discharge passage 27 is supplied through oil pressuresupplying passages 28, 29 into hydraulic chambers 16 a, 16 b of aboveeach hydraulic actuator 13, and is also supplied through main oilgallery 30 to various sliding sections or lubricating oil requiringsections in the engine.

As shown in FIG. 3, above oil pump 22 is of a general trochoid type andincludes pump housing 50 fixed to a side wall of a cylinder block (notshown) of the engine. Pump housing 50 accommodates therein inner rotor52 which is rotatably driven through pump shaft 51 which is rotatablydriven by the crank shaft. Outer rotor 53 is rotatably disposed insidepump housing 50 and has internal teeth which are engageable withexternal teeth of inner rotor 52. Pump chamber 54 is defined betweeneach internal tooth and each external tooth, corresponding to oneinternal or external tooth. The volume of pump chamber 54 is changed tomake pumping action. Above pump housing 50 is formed at its lower endsection with suction port 55 in communication with above suction passage23 and at its upper end section with discharge port 56 in communicationwith above discharge passage 24. Relief valve 38 is disposed at a lowersection of above discharge port 56 and will be discussed below.

Regarding above electric pump 25, electric motor 25 a is rotatablycontrolled in accordance with an engine operating condition under theaction of controller 31 as a controlling mechanism.

Above oil pressure supplying passages 28, 29 are respectively connectedwith supplying-draining passages 28 a, 29 a through which oil pressureis supplied to or released from hydraulic chambers 16 a, 16 b.Additionally, drain passages 32 a, 32 b are provided to release oilpressure from hydraulic chambers 16 a, 16 b. Supplying-draining passages28 a, 29 a and drain passages 32 a, 32 b are selected under the actionof electromagnetic selector valves 33, 34 which are respectivelydisposed in above oil pressure supplying passages 28, 29. Above oilpressure supplying passages 28, 29 respectively have check valves 35, 36which prevent reverse flow of the lubricating oil from hydraulicchambers 16 a, 16 b and are respectively disposed at the upstream sidesof electromagnetic selector valves 33, 34. Above electromagneticselector valves 33, 34 are arranged to carry out operation for selectingthe passages through spool valves disposed therein under the action of acontrol current from above controller 31.

First bypass passage 37 is provided at the side of above oil pump 22 soas to bypass oil pump 22. More specifically, this first bypass passage37 has an upstream end connected with above suction passage 23 and adownstream end connected with above discharge passage 24, so that firstbypass passage 37 is disposed to bypass oil pump 22. Relief valve 38 isconnected to first bypass passage 37 in parallel with oil pump 22 toregulate pressure of the lubricating oil discharged from oil pump 20 ata constant level. Check valve 39 is disposed at a position in parallelwith relief valve 38 to allow the lubricating oil to flow only in adirection of from the side of suction passage 23 to the side ofdischarge passage 24 in first bypass passage 37.

On the other hand, second bypass passage 40 is formed at the side ofabove electric pump 25 so as to bypass electric pump 25. Morespecifically, this second bypass passage 40 has an upstream endconnected with above second suction passage 26 and a downstream endconnected with above second discharge passage 27, so that second bypasspassage 40 is disposed to bypass electric pump 25. Bypass valve 41 isdisposed in second bypass passage 40 to be opened when electric pump 25stops in operation. This bypass valve 41 is adapted to be opened at alower pressure level than above relief valve 38.

Pilot pressure reducing valve 42 (or pressure reducing valve) isdisposed at the downstream side of second discharge passage 27 connectedwith above electric pump 25 to reduce the pressure of the lubricatingoil discharged to above main oil gallery 30 at a constant level.

Filter 43 is disposed between above discharge passage 24 and secondsuction passage 26. Above electric pump 25, second bypass passage 40,bypass valve 41, pilot pressure reducing valve 42 are fixedly installedto the cylinder block in such a manner of being connected with abovemain oil gallery 30.

Information or signals from various types of sensors such as an enginespeed sensor, an intake air amount sensor, a throttle valve openingdegree sensor, an engine coolant temperature sensor, or the like (notshown) are fed into above controller 31 so as to detect the engineoperating condition at present time upon calculation or the like incontroller 31. Subsequently, controller 31 produces the control currentsin accordance with the engine operating condition which control currentsare output to above electric motor 25 a and above electromagneticselector valves 33, 34.

Hereinafter, discussion will be made on operation of this embodiment. Atengine starting, the lubricating oil is low in temperature and high inviscosity. This increases flow resistance in an oil passage anddecreases the number of rotations of oil pump 22 thereby lowering oilpressure supplied to various sections of the engine. Consequently,electric motor 25 a is rotationally driven under the action of thecontrol current from controller 31 thereby rotatably driving electricpump 25. At this time, controller 31 does not apply current to aboveelectromagnetic selector valves 33, 34 so that these valves are in anopening state.

Therefore, the lubricating oil discharged from both pumps 22, 25, issmoothly increased in oil pressure and supplied through oil pressuresupplying passages 28, 29 to hydraulic chambers 16 a, 16 b, andadditionally, through main oil gallery 30 to the various slidingsections in the engine.

More specifically, each hydraulic actuator 13 is supplied with oilpressure so as to be able to be driven in accordance with a commandcurrent from controller 31. By this, variable valve lift mechanism 2becomes possible to make an optimum control in accordance with theengine operating condition immediately after the engine starting.Therefore, for example, in case of accomplishing rapid accelerationimmediately after engine starting, it is possible to obtain a goodacceleration characteristic upon control of variable valve liftmechanism 2 to a certain valve lift.

Thereafter, when engine speed rises so that the temperature of thelubricating oil is raised thereby making a shift to a normal operatingrange, the discharge pressure of the lubricating oil discharged underthe action of oil pump 22 becomes sufficiently high. Then, controller 31cuts off electric current supplied to electric motor 25 a so thatelectric pump 25 stops in operation. On the other hand, electric currentis supplied to electromagnetic selector valves 33, 34 so as to move eachspool valve inside electromagnetic selector valves 33, 34. This opensoil pressure supplying passages 28, 29 and drain passages 32 a, 32 b sothat oil pressure is supplied to one-side hydraulic chamber 16 b, 16 bwhile the lubricating oil within the other-side hydraulic chamber 16 a,16 a is discharged through drain passages 32 a, 32 b into oil pan 20. Asa result, each piston rod 17 is moved by a certain amount therebyrotationally driving each control shaft 11 by a certain degree in angle.By this, variable valve lift mechanism 2 controls a valve lift amount ofabove intake valves 1, 1 in a manner to gradually increase the valvelift amount.

In case that the engine speed rises thereby changing engine speed to ahigh speed range, a large amount of the lubricating oil is supplied intoeach hydraulic chamber 16 b, 16 b through above electromagnetic selectorvalves 33, 34 operated by controller 31, while the lubricating oil isdrained from each hydraulic chamber 16 a, 16 a. By this, control shaft11 is rotated the maximum in one direction so that variable valve liftmechanism 2 controls the valve lift of intake valves 1, 1 to the maximumvalve lift amount.

On the other hand, in case that the engine speed changes from a highspeed range to lower or medium speed range, electromagnetic selectorvalves 33, 34 are operated to select the flow passages. At this time,oil pressure is supplied to hydraulic chambers 16 a, 16 a, while oilpressure within hydraulic chambers 16 b, 16 b is released through drainpassages 32 a, 32 b. By this, each piston 15 moves back so as to rotatecontrol shaft 11 in an opposite direction. Therefore, variable valvelift mechanism 2 controls the valve lift of intake valves 1, 1 in amanner to gradually decrease to a small valve lift amount.

In this embodiment, in case that both oil pump 22 and electric pump 25are driven so that the lubricating oil discharged through oil pump 22 issucked in and discharged through electric pump 25, when the amount ofthe lubricating oil discharged by electric pump 25 becomes more thanthat by oil pump 22, the lubricating oil within oil pan 20 isautomatically flowed through the upstream end of bypass passage 37 andcheck valve 39 into the side of above discharge passage 24 and secondsuction passage 26, and then sucked in and discharged by electric pump25.

As a result, in addition to securely preventing generation of negativepressure between both pumps 22 and 25 or between discharge passage 24and second suction passage 26, in the structure of passages for thelubricating oil can refrain from being complicated so that cost risingcan be suppressed because only short bypass passage 37 for merelybypassing oil pump 22 is provided.

In case that pressure of the lubricating oil passed through oil pump 22or bypass passage 37 exceeds a certain level within above dischargepassage 24, relief valve 38 opens so as to allow the lubricating oil toflow into oil pan 20. As a result, an excessively high pressure can beprevented from being generated within above discharge passage 24.

As discussed above, in case that electric pump 25 is stopped in drivingunder the action of controller 31, the lubricating oil dischargedthrough oil pump 22 can be supplied from discharge passage 24 throughsecond bypass passage 40, bypass valve 41 and main oil gallery 30 to thevarious sliding sections, without increasing a driving load of oil pump22. Additionally, the lubricating oil can be supplied also through oilpressure supplying passages 28, 29 to hydraulic chambers 16 a, 16 b. Asa result, it is possible to secure good lubrication in the varioussliding sections and good control response in variable valve liftmechanism 2.

Furthermore, pilot pressure reducing valve 42 is disposed at thedownstream side of above second discharge passage 27 so that thelubricating oil at an excessively high pressure can be prevented frombeing supplied to the various sliding sections and hydraulic chambers 16a, 16 b.

FIGS. 4 and 5 illustrate another embodiment of the lubricating oilsupplying system according to the present invention, similar to theembodiment of FIGS. 1 to 3, with the exception that check valve 39 isassembled within relief valve 38 disposed to above bypass passage 37.

More specifically, relief valve 38 is formed with cylindrical retaininghole 60 (or a low pressure chamber) located at the inside of above pumphousing 50 and at the side of discharge port 56. Plunger valve body 62is slidably disposed inside above retaining hole 60 whose bottom sectionis closed with plug member 61. Pump housing 50 is formed with pressurereceiving chamber 63 located at a section above the tip end side ofabove retaining hole 60. Pressure receiving chamber 63 is incommunication with above discharge port 56 so as to be opened and closedwith a surface of top section 62 a of above plunger valve body 62. Valvespring 64 as a biasing member is springingly loaded between aboveplunger valve body 62 and plug member 61 so as to bias above plungervalve body 62 in a direction to close above pressure receiving chamber63.

Above retaining hole 60 has a lower section which is in communicationwith a downstream side (within oil pan 20) of above bypass passage 37through communicating passage 65.

Additionally, as shown also in FIG. 5, above plunger valve body 62 isformed with four communicating grooves 66 extending in an axialdirection of plunger valve body 62 and located at outer peripheralsurface thereof at interval of about 90 degrees (in angle) in peripheraldirection of plunger valve body 62. Each communication groove 66 has abottom surface of the arcuate shape in section. Consequently, whenplunger valve body 62 is moved back against the biasing force of valvespring 64, the lubricating oil within above pressure receiving chamber63 flows from the top surface of top section 62 a through eachcommunicating groove 66 to communicating passage 65, thereby beingreturned to the downstream side of bypass passage 37.

Furthermore, above check valve 39 is accommodated and disposed insidetop section 62 a of above plunger valve body 62.

This check valve 39 includes cup-shaped retainer 68 which ispress-fitted within valve hole 67 formed at the central portion of abovetop section 62 a. Retainer 68 accommodates and retains therein checkball 70 for opening and closing communicating hole 69 formed to pierce abottom wall of valve hole 67. Above retainer 68 is formed withthrough-hole 71 which is formed to pierce the central portion of theupper wall so as to be in communication with above pressure receivingchamber 63. Check ball 70 is biased in a direction to close abovecommunicating hole 69, by spring 72 (or a second biasing member) whichhas a sufficiently small spring force and is springingly loaded betweencheck ball 70 and the upper wall of retainer 68.

When the pressure of the lubricating oil discharged from above oil pump22 is not lower than a certain level, the lubricating oil flows throughabove discharge port 56 into pressure receiving chamber 63 therebypushing down plunger valve body 62 against the biasing force of valvespring 64. By this, the lubricating oil within pressure receivingchamber 63 flows through each communicating groove 66 into retaininghole 60 and then flows through communicating passage 65 to be drainedinto oil pan 20.

As a result, an excessive pressure rise at the side of discharge passage24 can be suppressed as discussed above.

Additionally, under this condition, communicating hole 69 can besecurely closed with above check ball 70 under the action of oilpressure within pressure receiving chamber 63 and transmitted throughabove through-hole 71 and of the biasing force of spring 72.

On the other hand, when the pressure of the lubricating oil dischargedfrom above electric pump 25 exceeds that from oil pump 22, thelubricating oil flows from bypass passage 37 through above communicatingpassage 65 into retaining hole 60. This lubricating oil raises checkball 70 against biasing force of spring 72 thereby opening communicatinghole 69.

As a result, the lubricating oil within oil pan 20 flows through bypasspassage 37 and check valve 39 into discharge passage 24 and secondsuction passage 26 thereby being sucked to and discharged from electricpump 25. Consequently, a negative pressure can be securely preventedfrom being generated between both pumps 22, 25.

Moreover, since above check valve 39 is assembled inside relief valve38, it is unnecessary to form a special oil passage for disposingtherein check valve 39. As a result, it becomes possible to furthersimplify a passage configuration and to reduce a production cost.

Hereinafter, discussion will be made on technical ideas comprehendedfrom the above embodiments.

(1) A lubricating oil supplying system for an internal combustionengine, which includes a lubricating oil storage section for storinglubricating oil. A driven pump is driven by the internal combustionengine to suck the lubricating oil from the lubricating oil storagesection and discharge the lubricating oil to a discharge passage. Anelectric pump is provided for sucking the lubricating oil dischargedfrom the driven pump to the discharge passage and discharge thelubricating oil to a lubricating oil requiring section in the internalcombustion engine. A controlling mechanism is provided for drivinglycontrolling the electric pump in accordance with a control signal. Abypass passage is provided for bypassing the driven pump. A check valveis disposed in the bypass passage to allow the lubricating oil in thelubricating oil storage section to flow only through a path bypassingsaid driven pump and toward side of the discharge passage.

With the above arrangement, when an amount of the lubricating oildischarged from the driven pump exceeds that from the electric pump, thelubricating oil within the lubricating oil storage section is flowedfrom the inlet of the bypass passage through the check valve into theside of the above discharge passage. Then, the lubricating oil is suckedin and discharged from the electric pump so as to be supplied to thelubricating oil requiring section. By this, a negative pressure can beprevented from being developed between the both pumps, while avoidingcomplication of a passage structure for the lubricating oil therebysuppressing a cost rise, because only the short bypass passage formerely bypassing driven pump is provided.

(2) In the technical idea of (1), the lubricating oil supplying systemfor an internal combustion engine further includes a relief valvedisposed in the bypass passage to allow the lubricating oil within thedischarge passage to flow to a lower pressure side when a dischargepressure of the lubricating oil discharged from the driven pump to thedischarge passage is not lower than a level.

With the above arrangement, when the pressure within the dischargepassage becomes not lower than the certain level, the relief valve opensto allow the lubricating oil to flow to the lower pressure side, so thatan excessively high pressure can be prevented from being developedwithin above discharge passage.

(3) In the technical idea of (2), the lubricating oil flowed out throughthe relief valve is returned into the lubricating oil storage section atthe lower pressure side. The check valve is disposed inside the reliefvalve to allow the lubricating oil to flow only through a path from thelubricating oil storage section to the side of the discharge passage.

With the above arrangement, the lubricating oil returned through therelief valve into the lubricating oil storage section can be againflowed into the discharge passage when the check valve opens.Additionally, since the above check valve is assembled inside the reliefvalve, it is unnecessary to provide a special oil passage to which thecheck valve is to be disposed. As a result, it can be possible tosimplify a passage configuration and to achieve a cost reduction.

(4) In the technical idea of (3), the relief valve includes a plungervalve body having a pressure receiving section formed at one end side ofthe plunger valve body. A section defining a lower pressure chamber isformed at the other end side of the plunger valve body to be incommunication with the lubricating oil storage section. A biasing memberis disposed in the lower pressure chamber to bias the plunger valve bodyin one direction. A part of the lubricating oil acting on the pressurereceiving section flows through the lower pressure chamber into thelubricating oil storage section when the plunger valve body movesagainst a biasing force of the biasing member. The check valve isdisposed in the pressure receiving section of the relief valve.

(5) In the technical idea of (2), the lubricating oil supplying systemfor an internal combustion engine further includes a second bypasspassage for bypassing the electric pump. A bypass valve is disposed inthe second bypass passage and adapted to open in accordance with apressure at the side of the discharge passage. The bypass valve isadapted to open at a pressure level lower than a pressure level at whichthe relief valve opens.

According to this idea, no lubricating oil is released to the lowerpressure side when the lubricating oil is supplied through the abovebypass valve to the lubricating oil requiring section. Therefore, theelectric pump can be prevented from being wastefully worked.

(6) In the technical idea of (1), the lubricating oil supplying systemfor an internal combustion engine further includes a second bypasspassage for bypassing the electric pump. A bypass valve is disposed inthe second bypass passage and adapted to open in accordance with apressure level at the side of the discharge passage.

According to this idea, the lubricating oil discharged from the drivenpump can be supplied from the discharge passage through the secondbypass passage to the lubricating oil requiring section withoutincreasing a driving load of the driven pump, even in case that theelectric pump is not driven.

(7) In the technical idea of (1), the lubricating oil supplying systemfor an internal combustion engine further includes a second bypasspassage for bypassing the electric pump. A bypass valve is disposed inthe second bypass passage and adapted to open when the electric pumpstops in driving.

According to this idea, operational effects similar those in the above(6) can be obtained.

(8) In the technical idea of (1), the lubricating oil supplying systemfor an internal combustion engine further includes a pressure reducingvalve for reducing a pressure of the lubricating oil supplied to thelubricating oil requiring section when a pressure at a section of fromthe electric pump to the lubricating oil requiring section is not lowerthan a level.

According to this idea, the lubricating oil at a high pressure exceedinga required level can be prevented from being supplied to the lubricatingoil requiring section, under the action of the pressure reducing valve.

(9) In the technical idea of (1), the lubricating oil requiring sectionincludes a main oil gallery for supplying the lubricating oil to slidingsections in the internal combustion engine, and a variable valveactuation mechanism operated by oil pressure. The electric pump isdriven by the controlling mechanism in accordance with an operatingcondition of the variable valve actuation mechanism.

It will be understood that this invention is not limited to theconfigurations in the above embodiments. For example, the driven pumpmay be a vane type in place of the above trochoid type. Additionally,one of the lubricating oil requiring section may be a driving apparatussuch as a valve timing controlling mechanism (variable valve timingmechanism) or the like controlled by oil pressure, other than variablevalve lift mechanism 2. Moreover, driving and stopping timings ofelectric pump 25 are not limited to a timing when the above enginestarting and a timing thereafter, so that it is possible to driveelectric pump 25 singly, for example, in case that oil pump 22 is introuble and failed in operation.

The entire contents of Japanese Patent Application No. 2004-293504,filed Oct. 6, 2004 is incorporated herein by reference.

1. A lubricating oil supplying system for an internal combustion engine,comprising: a lubricating oil storage section for storing lubricatingoil; a driven pump driven by the internal combustion engine to suck thelubricating oil from said lubricating oil storage section and dischargethe lubricating oil to a discharge passage; an electric pump for suckingthe lubricating oil discharged from said driven pump to the dischargepassage and discharge the lubricating oil to a lubricating oil requiringsection in the internal combustion engine; a controlling mechanism fordrivingly controlling said electric pump in accordance with a controlsignal; a bypass passage for bypassing said driven pump; and a checkvalve disposed in said bypass passage to allow the lubricating oil inthe lubricating oil storage section to flow only through a pathbypassing said driven pump and toward side of the discharge passage
 2. Alubricating oil supplying system for an internal combustion engine, asclaimed in claim 1, further comprising a relief valve disposed in saidbypass passage to allow the lubricating oil within the discharge passageto flow to a lower pressure side when a discharge pressure of thelubricating oil discharged from said driven pump to the dischargepassage is not lower than a level.
 3. A lubricating oil supplying systemfor an internal combustion engine, as claimed in claim 2, wherein thelubricating oil flowed out through the relief valve is returned intosaid lubricating oil storage section at the lower pressure side, whereinsaid check valve is disposed inside the relief valve to allow thelubricating oil to flow only through a path from said lubricating oilstorage section to the side of the discharge passage.
 4. A lubricatingoil supplying system for an internal combustion engine, as claimed inclaim 3, wherein the relief valve includes a plunger valve body having apressure receiving section formed at one end side of the plunger valvebody, a section defining a lower pressure chamber formed at the otherend side of the plunger valve body to be in communication with saidlubricating oil storage section, and a biasing member disposed in thelower pressure chamber to bias the plunger valve body in one direction,wherein a part of the lubricating oil acting on the pressure receivingsection flows through the lower pressure chamber into said lubricatingoil storage section when the plunger valve body moves against a biasingforce of the biasing member, wherein said check valve is disposed in thepressure receiving section of the relief valve.
 5. A lubricating oilsupplying system for an internal combustion engine, as claimed in claim2, further comprising a second bypass passage for bypassing saidelectric pump, and a bypass valve disposed in the second bypass passageand adapted to open in accordance with a pressure at the side of thedischarge passage, wherein the bypass valve is adapted to open at apressure level lower than a pressure level at which the relief valveopens.
 6. A lubricating oil supplying system for an internal combustionengine, as claimed in claim 1, further comprising a second bypasspassage for bypassing said electric pump, and a bypass valve disposed inthe second bypass passage and adapted to open in accordance with apressure level at the side of the discharge passage.
 7. A lubricatingoil supplying system for an internal combustion engine, as claimed inclaim 1, further comprising a second bypass passage for bypassing saidelectric pump, and a bypass valve disposed in the second bypass passageand adapted to open when said electric pump stops in driving.
 8. Alubricating oil supplying system for an internal combustion engine, asclaimed in claim 1, further comprising a pressure reducing valve forreducing a pressure of the lubricating oil supplied to the lubricatingoil requiring section when a pressure at a section of from said electricpump to the lubricating oil requiring section is not lower than a level.9. A lubricating oil supplying system for an internal combustion engine,as claimed in claim 1, wherein the lubricating oil requiring sectionincludes a main oil gallery for supplying the lubricating oil to slidingsections in the internal combustion engine, and a variable valveactuation mechanism operated by oil pressure, wherein said electric pumpis driven by said controlling mechanism in accordance with an operatingcondition of the variable valve actuation mechanism.
 10. A lubricatingoil supplying system for an internal combustion engine, as claimed inclaim 9, wherein the internal combustion engine is a multi-cylinderV-type engine in which the variable valve actuation mechanism isdisposed in each of banks.
 11. A lubricating oil supplying system for aninternal combustion engine, as claimed in claim 9, wherein the variablevalve actuation mechanism is a variable valve lift mechanism.
 12. Alubricating oil supplying system for an internal combustion engine, asclaimed in claim 9, wherein the variable valve actuation mechanism is avalve timing controlling mechanism.
 13. A lubricating oil supplyingsystem for an internal combustion engine, as claimed in claim 1, furthercomprising a filter disposed between said driven pump and said electricpump.
 14. A lubricating oil supplying system for an internal combustionengine, as claimed in claim 1, wherein said electric pump stops indriving when an engine speed rises.
 15. A lubricating oil supplyingsystem for an internal combustion engine, as claimed in claim 1, whereinsaid electric pump is driven when said driven pump is failed inoperation.
 16. A fluid pump comprising: a pump mechanism for suckingfluid from a storage section and discharging the fluid to a dischargesection; a plunger valve body having a pressure receiving section whichis formed at one end side of said plunger valve body and opens to thedischarge section, the plunger valve body being movable to release apart of fluid discharged from said pump mechanism to the dischargesection to a low pressure section; a section defining a low pressurechamber formed at the other end side of said plunger valve body and incommunication with the low pressure section; a biasing member disposedin the low pressure chamber to bias said plunger valve body in onedirection; and a check valve disposed in the pressure receiving sectionof said plunger valve body to allow the lubricating oil to flow througha path from said lower pressure chamber to the discharge section.
 17. Afluid pump as claimed in claim 16, wherein said check valve includes acheck ball for opening and closing a communicating hole formed in thepressure receiving section of said plunger valve body to communicate thelow pressure chamber and the discharge section, and a retainer fixed tothe pressure receiving section of said plunger valve body to accommodateand retain the check ball therein.
 18. A fluid pump as claimed in claim17, further comprising a second biasing member disposed within theretainer to bias the check ball in a direction to close thecommunicating hole.
 19. A fluid pump as claimed in claim 17, wherein theretainer is fixedly disposed within a valve hole formed in the pressurereceiving section of said plunger valve body.
 20. A lubricating oilsupplying system for an internal combustion engine, comprising: alubricating oil storage section for storing lubricating oil; a firstpump for sucking the lubricating oil from said lubricating oil storagesection and discharging the lubricating oil to a discharge passage; asecond pump for sucking the lubricating oil discharged from said firstpump to the discharge passage and discharging the lubricating oil to alubricating oil requiring section in the internal combustion engine; abypass passage for bypassing said first pump; and an opening and closingmechanism disposed in said bypass passage to open said bypass passagewhen an amount of the lubricating oil discharged from said first pumpexceeds that from said second pump, and to cutoff said bypass passagewhen the amount of the lubricating oil discharged from said first pumpis similar to that from said second pump or when the amount of thelubricating oil discharged from said second pump is lower than that fromsaid first pump.